Automatic ship hull surface modeling and hydrodynamic optimization

Das, Tanmoy (2013) Automatic ship hull surface modeling and hydrodynamic optimization. Masters thesis, Memorial University of Newfoundland.

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Abstract

Engineers have always been fascinated by the optimality of an objective function of interest. Hydrodynamicists in the ocean and naval architectural engineering field have always sought to improve the hydrodynamic performance of any floating structure. For a moving vessel, wave resistance is one of the most important properties of hydrodynamic performance, and it influences a ship voyage economically by significant effect on EHP or fuel consumption. Therefore, reduction in wave resistance of any ship will help in reducing fuel cost. -- The present study investigates the scope for optimization of ship hulls based on wave resistance by modifying their geometries. During modification, there are geometric constraints to be maintained required by design and operational criteria. -- The calculation of wave resistance is based on a numerical solution, where ship hull surface discretization is required. An automatic hull generation and discretization system was developed, where a table of offsets or general coordinates of ship hull can be used as input. Then, the process proceeds with the BFGS (Broyden-Fletcher-Goldfarb-Shanno) optimization algorithms integrated with three different hull geometry modification methods. MAPS Resistance Version 2.0 was utilized to calculate wave resistance (the objective function) inside the algorithm. -- An integrated program employing FORTRAN 90 was developed, which is able to represent a ship hull mathematically and graphically utilizing B-spline surface and IGES format, respectively. This system is also able to process an optimization algorithm with direct feedback from the resistance evaluation unit. It will produce different sets of modified ship hull shapes with improved wave resistance. Therefore, it can serve a variety of interests determined by needs of a project. -- Several types of ship hulls were developed and checked for geometric validation, and results were satisfactory. Two basic ship hulls (Wigley and Series 60 Hulls) were further investigated for their wave resistance coefficients with published experimental data, and the convergences of results were quite acceptable. The optimum hull forms obtained from the software show improved wave resistance with significant differences in coefficient of wave resistance (Cw) values for all the selected Froude numbers. This program has been prepared in such a way that it can be adopted to search for the minima of other objective functions.

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